You can announce HMVs in amv announcements like any normal AMV. Just warn about the content in the topic title/post and in the video description as well. Or do you guys mean you'd want a "Hentai Videos" thread in the recommended AMVs section?

Try doing a simple search for hentai and you'll find quite a bit. Or if you want to check out a place that has a good portion of videos (that I know of at least) all in one place you can check out the archive